In the relentless in-your-face power shower of the Edinburgh Fringe, Islander was a relaxing bath, with marine salts and probably candles because there was a power cut.

It’s an unusual, experimental musical piece which works against all expectations as a show with only two voices and no band or backing track, just an ingenious sound looping device.

Now in the intimate space of Southwark Playhouse, Bethany Tennick and Kirsty Findlay tell a story about isolation and distancing from ‘the mainland’ on some other-worldly folk singing Hebridean island, and through the a cappella vocalising you really can hear the sounds of the sea, the moaning of the wind and, rather beautifully, whale song of a creature trapped by the tides.

Even those of us resistant to magical realism – this year’s overdone meme at Edinburgh – fell under its spell because it walks a windswept ridge between myth and reality, citing the Orcadian folk tales of the Finfolk, a race of spirits who don’t trust mortals.

In the ‘real’ world, the islanders debate whether or not to be resettled to a Scotland with doctors, and schools, and more than one pub, and the conversations even in dialect are sharp and clear, especially Eilidh’s grandmother, one of the many characters portrayed by Findlay, who relishes pretending to be dead to frighten the grandkids.

‘I’m not playing’ she says. ‘This is a rehearsal’.

Although ten minutes too long, Islander most certainly isn’t a rehearsal, it’s a perfectly finished piece, like a stone polished by the waves.

until October 26